I was repairing and painting a secondhand bumper today for an Escort today. The bumper was red, and I was recolouring it to Amparo Blue.
It occured to me that probably a few members don't know there are various colours of primer (in the trade, they are called Value Shades - as they add 'value', or depth to the basecoat).
Essentially, there are 7 available (ranging from white, through grey to black), but realistically, in your average accessory shop you will only get the choice of white/grey/black.
It is very important to select the correct one for your car's colour, otherwise you will get a mismatch (or need to apply many more layers of basecoat - if you are lucky).
I have access to a trade-only website (sorry, I can't publish it), but if anyone cares to supply me with their paint code (as & when they need it), I will gladly tell them what colour of primer they should be using.
Incidentally, the 'red' pigmentation on the bumper was still showing through the grey primer (after 2 coats), so I sprayed it matt black, then another 2 coats of grey to get it right.
Bumper is now drying off (in blue), and if no further coats are needed, will be lacquered tonight!
Hope this is of some help.